1. Technical Field
The present invention generally relates to a semiconductor device. In particular, the invention relates to a semiconductor device that is formed over a flexible substrate, though not limited thereto.
2. Related Art
In recent research and development of various kinds of electro-optical devices such as a liquid crystal device and the like, the use of a flexible substrate as a component thereof has been studied. The flexible substrate has an advantage in that it is possible to make the size of an apparatus smaller. In addition, the flexible substrate achieves weight reduction. Moreover, the flexible substrate has another advantage in that it can offer flexibility as its name indicates while enhancing shock/impact resistance.
In the technical field to which the present invention pertains, for example, a technique for manufacturing a flexible TFT display device with the use of a metal foil as a substrate is described in JP-A-2004-109975. As another example of related art, a method for manufacturing an electro-optical device with the adoption of a transferring technique is described in JP-A-2006-245091. In addition, some applications of such a method for manufacturing an electro-optical device with the use of a transferring technique to a flexible display device is also described in the related-art technique of JP-A-2006-245091 mentioned herein.
The inventors of the present invention are engaged in the research and development of an electro-optical device that uses a flexible substrate as a component thereof with an aim to enhance the characteristics/performance of such a device.
For example, as a typical configuration of an active matrix substrate (hereafter may be referred to as an “array substrate”) that is used as a component of such an electro-optical device, a plurality of pixels each of which has a thin-film transistor (TFT) and a pixel electrode is arrayed in a matrix layout. An inorganic insulation film such as a silicon oxide film or a silicon nitride film is formed over the entire surface of a glass substrate. The inorganic insulation film formed on the surface of the glass substrate functions as an underlying insulation film. After the deposition of the underlying insulation film on the glass substrate, various kinds of films are laminated over the underlying insulation film so as to form the thin-film transistors and the pixel electrodes mentioned above.
However, a layer structure that includes thin-film transistors and pixel electrodes formed over the underlying insulation film that is deposited on the entire surface of a flexible substrate has the following disadvantages. The flexibility of the flexible substrate differs from the flexibility of the underlying insulation film. Because of a difference in flexibility therebetween, the underlying insulation film and the thin-film transistor formed over the underlying insulation film may get cracked when either mechanical stress or thermal stress is applied thereto. If such a crack occurs, the characteristics of a device deteriorate.